SOLUTION: A speedboat can travel at 20km per hour in still water. It takes the boat 3/5 as much time to travel 90km down river as it does to travel the same distance up river. Find the rate

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Question 783632: A speedboat can travel at 20km per hour in still water. It takes the boat 3/5 as much time to travel 90km down river as it does to travel the same distance up river. Find the rate of the river current in kilometers per hour.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
A speedboat can travel at 20km per hour in still water.
It takes the boat 3/5 as much time to travel 90km down river as it does to travel the same distance up river.
Find the rate of the river current in kilometers per hour.
:
Actually we can do this without knowing the distance. Use .6 for 3/5
Let r = rate of the river
then
(20-r) = effective speed up-river
and
(20+r) = effective speed down river
:
Write a distance equation, dist = time * speed
.6(20+r) = 1(20-r)
12 + .6r = 20 - r
.6r + r = 20 - 12
1.6r = 8
r = 8/1.6
r = 5 km/hr is the rate of the current